In the optical transmission field, for implementing optical signal transmission, optical signals of different wavelengths need to be multiplexed onto a fiber in a manner of wavelength division multiplexing, and then propagated in a form of wavelength division multiplexing signals. A receiving end extracts the optical signals of different wavelengths from the wavelength division multiplexing signals through a specific method, and then detects the strength of the optical signals and judges, according to the strength of the optical signals, the signal power or whether the signals are lost.
In early applications, an optical wavelength demultiplexer is generally used to separate the signals of different wavelengths from the wavelength division multiplexing signals transmitted in the fiber, and then strength of the signals of different wavelengths is measured.
With the development of technologies, a coherent receiving manner of wavelength division multiplexing signals emerges. The approach is that, optical signals of different wavelengths, which are sent by a local laser set at a receiving end, imposes interference onto the signals of different wavelengths in the wavelength division multiplexing signals. When the optical wavelength of the local laser is adjusted to coincide with the optical wavelength of the optical signal to be received, the optical signal to be received can be extracted from the wavelength division multiplexing signals. However, in this manner, the optical signal and a local oscillator signal are cohered in a frequency mixer and output together, and therefore, how to detect the power of the optical signal becomes a problem to be solved in the industry.